In the past many optical devices have been developed for determining the distances between a reference axis and points on an object and thereby deriving data on, for example, the thickness or shape of the object. One such device is found in U.S. Pat. No. 4,221,973 to Nosler which discloses a device employing optics for determining the position of a log in a plywood mill. Light from a laser is reflected off of the object and focussed onto a photodetector array by a lens. The distance from a reference axis to the point where the light is reflected on the log and thereby the diameter of the log, can be determined from the position where the light strikes the photodetector array.
Apparatuses are also known for monitoring and determining the instantaneous thickness of a moving strip of planar material simultaneously at several different positions. Such a device is disclosed in the U.S. Pat. No. No. 3,671,726 to Kerr. Here, light from a single source passes through a plurality of prisms, each of which reflects part of the light at right angles from the original beam towards the strip of material. The light from each prism strikes the object and is reflected towards a detector unit. Thus a plurality of detector units are required, one for each prism. Other such units employing a multitude of detector units have used an arc lamp and a plurality of optical fibers extending from the lamp towards the object.
An object of the present invention is to provide an apparatus capable of instantaneously determining the distances of a plurality of points on a moving strip from a reference axis while employing a minimum number of components for increased economy and reliability as well as ease of installation. It is a further object to provide a device capable of measuring closely spaced-apart points to provide more precise data on the object.